The present invention relates to chemical compounds that inhibit MKNK1 kinase (also known as MAP Kinase interacting Kinase, Mnk1) and MKNK2 kinase (also known as MAP Kinase interacting Kinase, Mnk2). Human MKNKs comprise a group of four proteins encoded by two genes (Gene symbols: MKNK1 and MKNK2) by alternative splicing. The b-forms lack a MAP kinase-binding domain situated at the C-terminus. The catalytic domains of the MKNK1 and MKNK2 are very similar and contain a unique DFD (Asp-Phe-Asp) motif in subdomain VII, which usually is DFG (Asp-Phe-Gly) in other protein kinases and suggested to alter ATP binding [Jauch et al., Structure 13, 1559-1568, 2005 and Jauch et al., EMBO J25, 4020-4032, 2006]. MKNK1a binds to and is activated by ERK and p38 MAP Kinases, but not by JNK1. MKNK2a binds to and is activated only by ERK. MKNK1 b has low activity under all conditions and MKNK2b has a basal activity independent of ERK or p38 MAP Kinase. [Buxade M et al., Frontiers in Bioscience 5359-5374, May 1, 2008]
MKNKs have been shown to phosphorylate eukaryotic initiation factor 4E (eIF4E), heterogeneous nuclear RNA-binding protein A1 (hnRNP A1), polypyrimidine-tract binding protein-associated splicing factor (PSF), cytoplasmic phospholipase A2 (cPLA2) and Sprouty 2 (hSPRY2) [Buxade M et al., Frontiers in Bioscience 5359-5374, May 1, 2008].
eIF4E is an oncogene that is amplified in many cancers and is phosphorylated exclusively by MKNKs proteins as shown by KO-mouse studies [Konicek et al., Cell Cycle 7:16, 2466-2471, 2008; Ueda et al., Mol Cell Biol 24, 6539-6549, 2004]. eIF4E has a pivotal role in enabling the translation of cellular mRNAs. eIF4E binds the 7-methylguanosine cap at the 5′ end of cellular mRNAs and delivers them to the ribosome as part of the eIF4F complex, also containing eIF4G and eIF4A. Though all capped mRNAs require eIF4E for translation, a pool of mRNAs is exceptionally dependent on elevated eIF4E activity for translation. These so-called “weak mRNAs” are usually less efficiently translated due to their long and complex 5′ UTR region and they encode proteins that play significant roles in all aspects of malignancy including VEGF, FGF-2, c-Myc, cyclin D1, survivin, BCL-2, MCL-1, MMP-9, heparanase, etc. Expression and function of eIF4E is elevated in multiple human cancers and directly related to disease progression [Konicek et al., Cell Cycle 7:16, 2466-2471, 2008].
MKNK1 and MKNK2 are the only kinases known to phosphorylate eIF4E at Ser209. Overall translation rates are not affected by eIF4E phosphorylation, but it has been suggested that eIF4E phosphorylation contributes to polysome formation (i.e. multiple ribosome on a single mRNA) that ultimately enables more efficient translation of “weak mRNAs” [Buxade M et al., Frontiers in Bioscience 5359-5374, May 1, 2008]. Alternatively, phosphorylation of eIF4E by MKNK proteins might facilitate eIF4E release from the 5′ cap so that the 48S complex can move along the “weak mRNA” in order to locate the start codon [Blagden SP and Willis A E, Nat Rev Clin Oncol. 8(5):280-91, 2011]. Accordingly, increased eIF4E phosphorylation predicts poor prognosis in non-small cell lung cancer patients [Yoshizawa et al., Clin Cancer Res. 16(1):240-8, 2010]. Further data point to a functional role of MKNK1 in carcinogenesis, as overexpression of constitutively active MKNK1, but not of kinase-dead MKNK1, in mouse embryo fibroblasts accelerates tumor formation [Chrestensen C. A. et al., Genes Cells 12, 1133-1140, 2007]. Moreover, increased phosphorylation and activity of MKNK proteins correlate with overexpression of HER2 in breast cancer [Chrestensen, C. A. et al., J. Biol. Chem. 282, 4243-4252, 2007]. Constitutively active, but not kinase-dead, MKNK1 also accelerated tumor growth in a model using Eμ-Myc transgenic hematopoietic stem cells to produce tumors in mice. Comparable results were achieved, when an eIF4E carrying a S209D mutation was analyzed. The S209D mutation mimicks a phosphorylation at the MKNK1 phosphorylation site. In contrast a non-phosphorylatable form of eIF4E attenuated tumor growth [Wendel H G, et al., Genes Dev. 21(24):3232-7, 2007]. A selective MKNK inhibitor that blocks eIF4E phosphorylation induces apoptosis and suppresses proliferation and soft agar growth of cancer cells in vitro. This inhibitor also suppresses outgrowth of experimental B16 melanoma pulmonary metastases and growth of subcutaneous HCT116 colon carcinoma xenograft tumors without affecting body weight [Konicek et al., Cancer Res. 71(5):1849-57, 2011]. In summary, eIF4E phosphorylation through MKNK protein activity can promote cellular proliferation and survival and is critical for malignant transformation. Inhibition of MKNK activity may provide a tractable cancer therapeutic approach.
WO 2007/025540 A2 (Bayer Schering Pharma AG) relates to substituted imidazo[1,2-b]pyridazines as kinase inhibitors, particularly PKC (protein kinase C) inhibitors, in particular PKC theta inhibitors.
WO 2007/025090 A2 (Kalypsis, Inc.) relates to heterocyclic compounds useful as inhibitors of Mitogen-activated protein kinase (MAPK)/Extracellular signal-regulated protein kinase (Erk) Kinase (abbreviated to “MEK”). In particular, WO 2007/025090 A2 relates inter alia to imidazo[1,2-b]pyridazines.
WO 2007/013673 A1 (Astellas Pharma Inc.) relates to fused heterocycles as inhibitors of Lymphocyte protein tyrosine kinase (abbreviated to “LCK”). In particular, WO 2007/013673 A1 relates inter alia to imidazo[1,2-b]pyridazines.
WO 2007/147646 A1 (Bayer Schering Pharma AG) relates to oxo-substituted imidazo[1,2-b]pyridazines as kinase inhibitors, particularly PKC (protein kinase C) inhibitors, in particular PKC theta inhibitors.
WO 2008/025822 A1 (Cellzome (UK) Ltd.) relates to diazolodiazine derivatives as kinase inhibitors. In particular, WO 2008/025822 A1 relates inter alia to imidazo[1,2-b]pyridazines as kinase inhibitors, particularly inducible T cell kinase (abbreviated to “Itk”) inhibitors.
WO 2008/030579 A2 (Biogen Idec MA Inc.) relates to modulators of interleukin-1 (IL-1) receptor-associated kinase (abbreviated to “IRAK”). In particular, WO 2008/030579 A2 relates inter alia to imidazo[1,2-b]pyridazines.
WO 2008/058126 A2 (Supergen, Inc.) relates inter alia to imidazo[1,2-b]pyridazine derivatives as protein kinase inhibitors, particularly PIM kinase inhibitors.
WO 2009/060197 A1 (Centro Nacional de Investigaciones Oncologicas (CNIO)) relates to imidazopyridazines as protein kinase inhibitors, such as the PIM family kinases.
U.S. Pat. No. 4,408,047 (Merck a Co., Inc.,) relates inter alia to imidazopyridazines having a 3-amino-2-OR-propoxy substituent having beta-adrenergic blocking activity.
WO 03/018020 A1 (Takeda Chemical Industries, Ltd.) relates to inhibitors against c-Jun N-terminal kinase, containing compounds which are, inter alia, imidazo[1,2-b]-pyridazines.
WO 2008/052734 A1 (Novartis AG) relates to heterocyclic compounds as antiinflammatory agents. In particular said compounds are, inter alia, imidazo[1,2-b]pyridazines. The compounds are useful for treating diseases mediated by the ALK-5 and/or ALK-4 receptor, and are also useful for treating diseases mediated by the PI3K receptor, the JAK-2 receptor and the TRK receptor.
WO 2008/072682 A1 (Daiichi Sankyo Company, Limited) relate to imidazo[1,2-b]pyridazine derivative which has an action of inhibiting TNF-alpha production, exerts an effect in a pathological model of inflammatory disease and/or auto-immune disease.
WO 2008/079880 A1 (Alcon Research, Ltd.) relates to 6-aminoimidazo[1,2-b]pyridazine analogues as Rho-kinase inhibitors for the treatment of glaucoma and ocular hypertension.
WO 2009/091374 A2 (Amgen Inc.) relates to fused heterocyclic deriviatives. Selected compounds are effective for prophylaxis and treatment of diseases, such as hepatocyte growth factor (“HGF”) diseases.
In J. Med. Chem., 2005, 48, 7604-7614, is an article entitled “Structural Basis of Inhibitor Specificity of the Protooncogene Proviral Insertion Site in Moloney Murine Leukemia Virus (PIM-1) Kinase”, and discloses, inter alia, imidazo[1,2-b]pyridazines as inhibitor structures used in the study described therein.
In J. Med. Chem., 2010, 53, 6618-6628, is an article entitled “Discovery of Mitogen-Activated Protein Kinase-Interacting Kinase 1 Inhibitors by a Comprehensive Fragment-Oriented Virtual Screening Approach”, and discloses, inter alia, in Table 1., some specific imidazo[1,2-b]pyridazines as compounds identified as MKNK-1 inhibitors.
In Cancer Res Mar. 1, 2011, 71, 1849-1857 is an article entitled “Therapeutic inhibition of MAP kinase interacting kinase blocks eukaryotic initiation factor 4E phosphorylation and suppresses outgrowth of experimental lung mestastases”, and discloses, inter alia, that the known antigfungal agent Cercosporamide is an inhibitor of MKNK1.
However, the state of the art described above does not describe the specific amino-substituted imidazopyridazine compounds of general formula (I) of the present invention as defined herein, i.e. an imidazo[1,2-b]pyridazinyl moiety, bearing:                in its 3-position, a:        
group;                in its 6-position, a group of structure:        
wherein:                * indicates the point of attachment of said group with the rest of the molecule,        R1 represents a C3-C6-cycloalkyl group which is optionally substituted with one or more substituents as defined herein, and        R2 represents a hydrogen atom or a substituent as defined herein;or a stereoisomer, a tautomer, an N-oxide, a hydrate, a solvate, or a salt thereof, or a mixture of same, as described and defined herein, and as hereinafter referred to as “compounds of the present invention”, or their pharmacological activity.        
It has now been found, and this constitutes the basis of the present invention, that said compounds of the present invention have surprising and advantageous properties.
In particular, said compounds of the present invention have surprisingly been found to effectively inhibit MKNK-1 kinase and may therefore be used for the treatment or prophylaxis of diseases of uncontrolled cell growth, proliferation and/or survival, inappropriate cellular immune responses, or inappropriate cellular inflammatory responses or diseases which are accompanied with uncontrolled cell growth, proliferation and/or survival, inappropriate cellular immune responses, or inappropriate cellular inflammatory responses, particularly in which the uncontrolled cell growth, proliferation and/or survival, inappropriate cellular immune responses, or inappropriate cellular inflammatory responses is mediated by MKNK-1 kinase, such as, for example, haematological tumours, solid tumours, and/or metastases thereof, e.g. leukaemias and myelodysplastic syndrome, malignant lymphomas, head and neck tumours including brain tumours and brain metastases, tumours of the thorax including non-small cell and small cell lung tumours, gastrointestinal tumours, endocrine tumours, mammary and other gynaecological tumours, urological tumours including renal, bladder and prostate tumours, skin tumours, and sarcomas, and/or metastases thereof.
The state of the art described above does not suggest that the specific amino-substituted imidazopyridazine compounds of general formula (I) of the present invention as defined herein would be so active as inhibitors of MKNK-1 kinase.